Production of high vacua by gettering



Oct. 25, 1960 M. E. HAINE ETAL PRODUCTION OF HIGH VACUA BY GETTERINGFiled Oct. 10. 1958 16 )Vl/CHA'EL RONALD M BL 00/1457? E /c 14 F1? F A'TTQH/VEK ted tems Far 2,957,619 PRODUCTION OF HIGH VACUA BY GETTERINGMichael Edward Haine, *Sulhamstead, and Ronald Noel Bloomer and EricWilliam Raymond Francis, Reading, England, assignors to Siemens EdisonSwan Limited, London, England, a'British company Filed Oct. 10, 1958,Ser. No. 766,445 Claims. c1. 230-69 This invention relates to theproduction of high vacua utilising the cleaning-up action on residualgases of certain materials known as getters. I 7

It is well known that a high vacuum can be produced in an enclosed spaceby the use of a getter following the removal of the greater part of thecontained atmosphere by a pump. A getter is a chemically activematerial, usually a metal, which combines withgases impinging upon it.It thus removes them from the gas phase, and holds them in chemicalcombination. In one form of getter, the reaction which takes place onthe getter surface is follower by diifusion of the unused gettermaterial through the layer of reaction products to the outer surface, sothat gettering continues until the whole bulk of the material is usedup. An example of such a getter process is barium interacting withoxygen gas.

Titanium may also be used as a getter. In the case of titanium, thediffusion process is very limited, and when a thin surface layer of thetitanium has become saturated the gettering action ceases. To overcomethis limitation, the titanium can be continuously evaporated onto thegettering surface, so that, when the surface of the getter becomessaturated, it is immediately covered with a fresh layer of titaniumwhich in turn can take up more gas. Adequate evaporation is achieved byheating a quantity of the material to a temperature just above itsmelting point so that it evaporates, and by continuously replenishingthe melt with material from the solid state. This process presentdifiiculties in the case of titanium, because, in the molten state, itis extremely reactive and it is difficult to find a suitablenon-reactive crucible or hearth from which to evaporate it.

The object of the present invention is to provide a means ofcontinuously presenting a clean metal surface for the getter reaction toproceed continuously.

According to the invention the surface of the getter material iscontinuously subjected to erosion whereby the gas saturated outer layeris removed, thus rendering the gettering reaction continuous. Theerosion is conveniently effected mechanically e.g. by subjecting thegetter material to abrasion, scraping or the like.

In one application of the method using titanium as the getter, aboat-shaped sheet of titanium containing a small quantity of coarsecarborundum grains is mounted in a glass bulb and incorporated into avacuum system. When "the bulb is shaken so that the abrasive grainsslide back and forth along the titanium sheet from end to end, acontinuous gettering action is obtained. When the shaking is stopped,the gettering action ceases after a short time interval.

To utilise the method in practice, an abrading action may be obtained byrubbing an abrading surface on a block or sheet of the getter material,which may be titanium or any other metal, metal alloy or mixture.Alternatively, grains of an abrasive may be placed inside a hollow drumof the getter material, and the drum rotated.

The invention will now be described with reference to the accompanyingdrawings, in which:

Fig. 1 shows an apparatus for applying the invention to the evacuationof a cathode ray tube,

Fig. 2 illustrates an alternative manner for effecting the abrasiveaction of the getter material;

Fig. 3 is an end view of the abrasive drum employed in the arrangementof Fig. 2,

Fig. 4 is a cross-section of the drum as shown in Fig. 2 to an enlargedscale.

Referring to the drawings, a cathode ray tube 1 to be evacuated ismounted in a suitable support 2 and is connected by way of itsevacuating tubulation 3 and an-intermediate connection 4 to a vacuumpump 5. The intermediate connection 4 and the evacuating tubulation 3may be removably connected by means of a rubber sleeve 6. The removal ofthe major portion of the gaseous molecules enclosed in theenvelope ofthe cathode ray tube 1 is effected by the vacuum pump 5, and theresidual portion thereof is removed by means of getter material 6',located in the intermediate connection 4, afterthe cathode ray tubeenvelope and the intermediate connection have been isolated from thepump by closure of valve 4'.

In order to maintain the effectiveness of the getter material 6,according to the invention, the surface of the getter material iscontinuously subjected to an abrasive action by means of a metal part 7having an abrading surface 8 in the nature of file teeth which rests onthe surface of the getter '6 and is moved to and fro by means of amagnet 9 located outside the intermediate connection 4. By moving themagnet 9 back and forth, the surface particles of the getter material 6'which have chemically combined with the residual gaseous molecules arecontinuously removed by the abrasive action of the metal part 7, therebyexposing a clean surface of the getter to the action of the residualgas.

The getter material may conveniently be in the form of a sheet or blockof titanium or any other reactive metal alloy or mixture which iscapable of exercising a gettering action on the residual gas in theenclosed space formed by the envelope of the cathode ray tube 1, and theintermediate connection 4.

In order to avoid the necessity for movement of the magnet 9 back andforth, an arrangement such as that shown in Figs. 2, 3 and 4 may beadopted. In this arrangement the getter material and the abrasive deviceare located in a chamber 10 communicating with the intermediateconnection 4. The abrading device is in the form of a conical drum 11against which blocks 12 of the getter material are adapted to rest,being prevented from movement when the drum 11 is rotated by providinginternal projections 13 on the wall of the chamber 10. The drum ismounted in a bearing 14 supported by the inner wall of the closed end ofthe casing 10 and is provided with diametrically extending armatures 15of magnetic material. A U-shaped magnet 16 is arranged with its limbsaround the external periphery of the chamber 10 and is arranged to berotated by a belt 17. As the magnet 16 is rotated, the magnetic fieldfrom the pole pieces thereof co-operating wtih the armatures 15 effectsthe rotation of the drum 11 and effects continual abrasion of thesurface of the blocks 12 of getter material.

Portions 11' of the periphery of the drum are made of foraminatedmaterial so as to expose the surface of the getter material to theaction of the residual gas contained in the system.

It will be appreciated that, in the interests of economy and long life,the abrasive action should remove only the thin surface layer which hasbecome saturated. Naturally, if more than this is removed, all the freshsurfaces so formed still contribute to the overall pumping action. 7

contact with and movable relativetothe'surface' of getter material onsaidsupporting meanswhereby continually to expose a fresh surface ofsuch getter material to the action of said-residual gas.

2. In apparatus for removing residual gas'frornan enclosed spaceincluding a getter material located in said space and exposed to theaction of residual gas therein, said getter material being capable ofchemical combination with said residual gas, an abrasive deviceincontact with said gettermaterial; and means located outside said spacefor continually'moving said device whereby to remove from the surface ofsaid getter material particles thereof. which havechemically combinedwith said residual gas; thereby exposing the clean surface of saidgetter material to the action of said gas.

3. Apparatus for avacuating an enclosed space comprising a vacuumpump,,an intermediate connection connected between said pump and saidenclosed space, a

getter material located in said connection, an abrasive device movablysupported in contact with said getter material, and means for causingrelative movement betweensaid getter material and said abrasive device.

4. Apparatus for evacuating an enclosed space comprising a vacuum pump,an intermediate connection connected between said pump and said enclosedspace, a getter material located in said connection, an abrasive devicein contact with and movable relative to said getter material, and meanslocated outside said connection for continually moving said abrasivedevice.

5. Apparatusfor evacuating an enclosed space comprising a vacuum pump,an intermediate connection between said-pumpand said enclosed space, achamber communicating with said intermediate'connection, a gettermaterial located in said chamber, a rotatably mounted abrasive devicelocated in said chamber in contact with and movable-relative to saidgetter material, a magnetic armature carried by said abrasive device, amagnet located outside said chamber and having pole pieces cooperatingwith said armature, said magnet being rotatably mounted co-axially withsaid abrasive device, and means for rotating'said' magnet to causerotation of said abrasive device by'interactionbetween said pole piecesand said armature.

. References Cited in the file of this patent UNIT ED STATES PATENTS2,636,664 Hertzler' Apr. 28, 1953

